Mechanisms of the Photodissociation of Aminoazobenzene Rydimers into Monomers, According to Data from Ultrafast Laser-Probing Spectroscopy

The results from ultrafast laser-probing spectroscopy of photoexcited states of trans -aminoazobenzene ( t -AAB) by means of ultrafast transient lens (UTL) and transient absorption spectroscopy (TAS) are analyzed. The analysis relies on earlier elaborated views of the rydimeric structure of azo dyes. It is shown that earlier reported UTL and TAS signals of aminoazobenzene (solutions in ethanol and heptanol) obeying the same laws of kinetic attenuation (a drop in the photo-induced refractive index of solvents for UTL and transient photoexcited Vis states of the dye for TAS) are in reality the mechanism of rydimer dissociation into two monomeric pairs. One of these pairs (consisting of neutral monomers) relaxes into the initial t- AAB 2 rydimer according to two exponential kinetic curves with constants (characteristic times) of 0.7 and 2 ps (UTL) or 0.6 and 1.9 ps (TAS). The other pair consists of a t- AAB monomer and a monomer with two phenylaminyl-type cations and Vis absorption at 600–750 nm; it undergoes trans – cis isomerization according to a mono-exponential kinetic law with constants of 0.3 ps (UTL) and 0.2 ps (TAS).